Disproportionation of alkoxy silane



United States Patent DISPROPORTIONATION OF ALKOXY SILANE DERIVATIVES Charles E. Erickson, Ithaca, and George H. Wagner, Clarence, N. Y., assignors, by mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York No Drawing. Original application April 22, 1948, Serial No. 22,703, now Patent No. 2,627,451, dated February 3, 1953. Serial N 0. 281,055

3 Claims. c1. zoo-448.8

Various schemes for the preparation of chlorosilane compounds include, as the initial step, a reaction between heated hydrogen chloride and silicon in the presence of a catalyst such as copper. The principal product is usually trichlorosilane, SiHCls; but other products are formed, including a minor proportion of dichlorosilane, SiHzClz. The latter compound is particularly useful in many syntheses, and in some cases it would be economically desirable to prepare it from the trichloro compound, even though only moderate efficiencies could be attained in the conversion. The present invention relates to such a conversion, and to analogous operations on other silane derivatives.

We have found that trichlorosilane can be disproportionated, with a redistribution of the hydrogen and chlorine atoms in such a way that considerable quantities of dichlorosilane are formed. Such disproportionation is effected by heating the trichlorosilane at a temperature above that sufiicient to reflux, and preferably at a temperature of 300 C. or above. The presence of an acid metal halide catalyst, such as AlCls, AlBla, FeCla, BF3, etc., promotes the efliciency of this reaction, and since the requisite temperatures are above the boiling point of SiHCls, it is convenient to seal the latter in a pressure vessel with the catalyst before applying heat, or to pass the vapors of SiHCl3 continuously over a bed of the catalyst.

The following table exhibits the results obtained in such operations, using charges of 100 cc. of SiHCla in a 300 cc. vessel, and varying the quantity of catalyst (AlCls), the time, and the temperature as indicated:

It will be noted that yields of SiHzClz as high as can be obtained in times of two hours or less, at temperatures above 300 C. The product also contains unchanged SiI-ICls which can be recovered and reprocessed.

The following data shows that the disproportionation will proceed, although at a slower rate, in the absence of a catalyst. This data was obtained in the same apparatus used in the aforesaid catalyzed reaction, with variations in temperature and time as indicated, and with other conditions identical, except for the omission of the catalyst.

Divided and this application April 7, 1952,

'ice

Some aspects of the process are suggested by the equation 2SiHC13- SiHzClz SiCLi but the picture given thereby is obviously an incomplete one. Several other products are formed, though in smaller proportion.

The process can also be applied to the trialkoxy silanes to form mixtures of the dialkoxy and tetralkoxy compounds, together With by-products. In this case the reaction goes readily at reflux temperature (l30-135 C.). In one experiment 16% of diethoxy silane was obtained when 56 grams of triethoxy silane were refluxed for six hours with 0.1 gram AlClz present, and, under similar conditions, di-isopropoxy silane was made by heating the tri-isopropoxy derivative.

While the disproportionation of iii-substituted silanes has been stressed herein because it appears to have more important industrial applications under present conditions, the diand mono-substituted silanes can also be disproportionated under similar conditions, and with the same catalysts. In each case the product contains compounds in which the ratio of substituent to silicon is respectively lower and higher than in the material taken. Thus, the unsubstituted silane is usuallyformed to some extent.

This application is a division of our copending application Serial No. 22,703, filed April 22, 1948, now U. S. Patent 2,627,451.

We claim:

1. Process of disproportionating a trialkoxy silane, to form the corresponding dialkoxy silane, which comprises heating the trialkoxy silane to a temperature of about C. to C., in the presence of an acid metal halide catalyst.

2. Process of disproportionating a trialkoxy silane, to form the corresponding dialkoxy silane, which comprises heating the trialkoxy silane to a temperature of about 130 C. to 135 C., in the presence of an aluminum chloride catalyst.

3. Process of disproportionating triethoxy silane to form diethoxy silane, which comprises heating the triethoxy silane to a temperature of about 130 C. to 135 C. in the presence of an acid metal halide catalyst.

References Cited in the file of this patent UNITED STATES PATENTS Hance Nov. 21, 1950 Hunter Jan. 20, 1953 Erickson Feb. 3, 1953 

1. PROCESS OF DISPROPORTIONATING A TRIALKOXY SILANE, TO FORM THE CORRESPONDING DIALKOXY SILANE, WHICH COMPRISES HEATING THE TRIALKOXY SILANE TO A TEMPERATURE OF ABOUT 130* C. TO 135* C., IN THE PRESENCE OF AN ACID METAL HALIDE CATALYST. 